Thin films of gallium nitride crystals has attracted much attention for use in superior blue light emitting devices, which have been commercialized as light-emitting diodes and are expected as semiconductor laser device emitting blue-purple rays for optical pickups. As methods for growing gallium nitride single crystals by Na-flux method, for example, according to “Jpn. J. Appl. Phys.” Vol. 42, (2003) page L4 to L6, the atmospheric pressure was 50 atms in the case of using nitrogen atmosphere and the total pressure was 5 atms in the case of using gas mixture atmosphere of 40 percent of ammonia and 60 percent of nitrogen.
Further, for example, according to Japanese patent publication 2002-293696A, gas mixture of nitrogen and ammonia is used to maintain a pressure of 10 to 100 atms. According to Japanese patent publication 2003-292400A, the pressure of atmosphere during the growing process is lower than 100 atms, and 2, 3 or 5 MPa (about 20, 30 50 atms) in the examples. Further, according to each of the prior arts, the growing temperature is lower than 1000° C. and lower than 850° C. in all the examples.